Thermal right, land left

Install a strain gauge internal to the fuselage right up against the hook
mount. Get Peter Masak to design a simple circuit that trips an electronic
relay when the strain exceeds a certain amount. Knowing Peter, it should take
him less than an hour.

Jim Vincent

I've been thinking about how to measure strain on the
rope during auto-tow, but this time from the auto side, not the
glider side.

I'm planning to tow using a 50# spring scale, and never exceed
40#, and see how long (far) it takes to accelerate to rotation
speed. For 500#, I seem to get calculations near to 1000ft or so.
I'd like to see if a 40# thrust AMT turbine would accelerate
a 500# glider to rotation in a reasonable runway length
(say 2000 ft or less).

As a second issue, I'm wondering if anyone has measurements of
the typical strain on a winch or auto tow rope. I'm
guessing .5 to .9 times the glider weight (probably near the
highest altitude right before release, right?).

Spring-type weight measuring devices for up to around hundreds of
pounds are in the $200 range. In the 500#+ range, though, things
get pricey...



--

------------+
Mark Boyd
Avenal, California, USA

"Mark James Boyd" wrote in message
news:4057718f$1@darkstar...
Install a strain gauge internal to the fuselage right up against the hook
mount. Get Peter Masak to design a simple circuit that trips an
electronic
relay when the strain exceeds a certain amount. Knowing Peter, it should
take
him less than an hour.

Jim Vincent

I've been thinking about how to measure strain on the
rope during auto-tow, but this time from the auto side, not the
glider side.

I'm planning to tow using a 50# spring scale, and never exceed
40#, and see how long (far) it takes to accelerate to rotation
speed. For 500#, I seem to get calculations near to 1000ft or so.
I'd like to see if a 40# thrust AMT turbine would accelerate
a 500# glider to rotation in a reasonable runway length
(say 2000 ft or less).

As a second issue, I'm wondering if anyone has measurements of
the typical strain on a winch or auto tow rope. I'm
guessing .5 to .9 times the glider weight (probably near the
highest altitude right before release, right?).

Spring-type weight measuring devices for up to around hundreds of
pounds are in the $200 range. In the 500#+ range, though, things
get pricey...



--

------------+
Mark Boyd
Avenal, California, USA

Much cheaper is a old-style (no vacuum assist) automobile master cylinder
and a hydraulic pressure gauge - or various junkyard parts to that effect.
Rent a 2000 pound scale to calibrate it.

Best launch winch or auto is a line tension of 1.0 x takeoff weight for the
whole launch. (Assumes the winch/tow-car driver and pilot know what they
are doing.)

Bill Daniels

Bill Daniels

Probably my explanation was not good enough. The airbrake microswitch and
the switch of the pressure transducer are in series. However with no
pressure (glider on the ground) the switch of the pressure transducer is
closed and opens reluctantly when pressure comes on (glider rolling for take
off). So this system gives a warning for airbrakes unlocked (or open) prior
to take off; it does not give an alert when flying with normal speed and
airbrakes open.
See my figure 5 of http://home.wxs.nl/~kpt9/gear.htm

Karel, NL


"Eric Greenwell" schreef in bericht
...
Todd Pattist wrote:
"K.P. Termaat" wrote:


The solution for a warning on air brakes unlocked prior to take off is
quite
easy. Use a micro switch on the air brake handle and a pressure
transducer

from a washing machine in series.

I'm confused as to why you need a pressure transducer. Just
put a microswitch on the Tost that detects the presence of
the towring, and wire that in series with the existing
sensor on the airbrakes. The airbrake sensor provides power
to both the gear sensor switch and the Tost sensor switch.
They both send power to the buzzer. If the brakes are
opened with the gear up or the ring inserted, your buzzer
goes off. Conversely, if the brakes are open and the ring
is inserted for the tow the buzzer sounds. Why wait until
you are rolling or in the air to sound the buzzer?
Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

The pressure sensor would be great for a self-launching sailplane. It
would also avoid alerting when the pilot had the spoilers open purposely
at the start of the launch, as some pilots do to avoid wing drop or
running over the towrope. An alert in those situations might not be a
bad thing, as it would test the system, and the pilot would be fully
aware that he was causing it.
--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Eric Greenwell wrote:
Jon Meyer wrote:

I'm saying it must be smaller to be cheaper. Bigger costs money.

Here was an important goal: "substantially lower costs than then-current
new gliders". It's the first one on the list in the history section of
the World Class Soaring Association (www.wcsa.org/history.htm).

A big part of this was to achieve "cheap".

Fixed undercarriage, no waterballast, even the requirement
for no flaps, are in my opinion all unnecessary requirements
for a world class glider,

If you want cheap, you have to leave off the things that make it costly.

Having seen three used PW-5's/Russias in the past year for
half the price of an LS-4, cost is an issue...

I'd also have to classify myself not as a soaring performance
enthusiast, but as a soaring consumer. Sort of like I'd
have a boombox instead of a six-speaker Bose, a 32" TV instead of HDTV,
etc. As a soaring consumer, I fit what Carl Herold has profiled:
doing X-C in 1-2 years in the sport, having soaring as a hobby,
etc.

As a consumer, I'm thrilled about the NON-performance aspects of soaring
that the PW-5, Russia, and Sparrowhawk provide.
Namely, lower cost, lighter weight, simpler features, modern
technology (which does not necessarily mean better performance).

Having lighter wings to assemble, a smaller trailer, shorter
wings, no flaps/gear/water ballast certainly are not things
that help performance, they only appeal to me as a consumer/hobbyist.

I can completely understand why the soaring enthusiasts would be baffled
at anyone who wants a new glider which performs worse than
the top 50% of gliders in the world. From their perspective,
which is perfectly understandable, this is absurd.

But if you eliminate the word "performance," every single
aspect now goes the other way. This is what I as a
soaring "consumer" look for in value.

Model aircraft builders have a similar quandry. The motor
airplane builders enjoy much more performance, but the
electric models are much easier to start, cleaner, and
less expensive. Electric model aircraft are gaining a lot of
popularity with "consumers."

I don't expect a Yugo to be appreciated by Ferrari drivers...
But you can drive a Yugo by the Ferrari shop AND the
gas station every day...

I don't think the World Class will ever draw pilots out of their
retract gliders in any numbers. The fixed gear and low cost
(read short wings) simply can never challenge span and
reduced drag. The World Class is a consumer class, and I
don't expect the enthusiasts to accept reduced performance...

On another note, I would like to see the World Class develop in
2009. One change perhaps is the "homebuild" option. This may
have discouraged some entries, and I'm not sure added any benefit
(another poster said this too). I would also like to
see a 36:1 or better glide as a minimum. I think the Sparrowhawk
Russia, Apis and Silent all have the potential to compete
with only minor modifications (different wings, changes to eliminate
flaps, different landing gear designs, etc.). And a lot of
improvement can happen given five years...

Will any of this now attract soaring "enthusiasts" to trade in their LS-4s?
I don't think so. But hey, I'm comfortable with that...

--

------------+
Mark Boyd
Avenal, California, USA

Dave Martin wrote:

We now seem to be advocating warnings and buzzers for
every eventuality. This is a list of the sounds a pilot
is expected to cope with if everyones idea are translated
into reality, it may not be complete..........

Under carriage
Flaps
Stall alert (2 one for each wing tip)
Tail dolly
Low battery
Canopy
Main Pin
G Meter
Spoiler alert
Aircraft Proximity alarm (only good if everyone has
one fitted)
Tyre pressure alert
Brake pad wear alert

Add to this one essential noise

Vario

And a few helpful ones

Radio
GPS alerts
Turn point alerts
Approaching airspace alerts on nav aides

Nope. I'm only interested in the buzzer that
warns against the problem that caused 50% of the
glider fatalities in the last 10 years.

Only one line on your list does that...

You can keep the rest...

true to form I've not even had an audio Vario in the past year
--

------------+
Mark Boyd
Avenal, California, USA

In article ,
Ben Flewett wrote:

We have a problem in that we have committed to the
PW5 until 2009 but perhaps there is something that
can be done here - some suggestions have already been
made as a result of this discussion.

Now THAT is a completely true statement. I must say I'm
remarkably pleased there was as much discussion as I've seen.
This can ONLY improve the participation and decision
in 2009. And that isn't too far off, so get your
opinions to the IGC soon, and start designing and building
your World Class entry...
--

------------+
Mark Boyd
Avenal, California, USA

I was thinking that the winch driver would see the glider airspeed via
telemetry and thus control it precisely and the pilot would control the
tension with a panel mounted meter. That way the pilot gets the right
airspeed and precisely loads the glider and cable to whatever value he feels
comfortable with up to the breaking strength of the weak link.

Bill,

Actually, I did this last year. I took an old radio control transmitter,
mounted it in a small box, and put one control potentiometer on a thumb wheel
mounted to a hand grip. In the winch, I have the receiver with a servo mounted
to the window in front of me. The servo has a long orange stick attached.

If the pilot wants to go faster, he thumbs forward, which moves the servo and
flag up. If slower, then down. If good, then horizontal.

Haven't tried it yet, but it was a fun project!


Jim Vincent
CFIG
N483SZ
illspam

On 16 Mar 2004 13:28:47 -0800, (Mark James Boyd)
wrote:


I've been thinking about how to measure strain on the
rope during auto-tow, but this time from the auto side, not the
glider side.

No need to measure anything - maths are completely sufficient to
calculate this.

In level flight the drag of a glider is

(1) drag = weight / (L/D)

example: 500lbs glider, L/D is 40, drag will be 12.5 lbs. This will be
also the strain on the tow rope in level flight. Adjusting this
formula for a climb is simple.


I'm planning to tow using a 50# spring scale, and never exceed
40#, and see how long (far) it takes to accelerate to rotation
speed. For 500#, I seem to get calculations near to 1000ft or so.
I'd like to see if a 40# thrust AMT turbine would accelerate
a 500# glider to rotation in a reasonable runway length
(say 2000 ft or less).

Aircraft weight: 500 lbs
Engine thrust: 40 lbs
Liftoff speed: 34 kts

(2) F = m * a. F = engine thrust
m = glider weight
a = acceleration

(3) a = F/m F = 177.6 N = 40 lbs
m = 226 kg = 500 lbs
- a = 0.79 m/s^2

(4) v = a * t v = liftoff speed (22.2 meters/sec = 34 kts)
t = time to reach v

(5) t = v / a

- t = 28.1 seconds

(s) s = 0.5 * a * t^2 s = distance covered (during t = 28.1 seconds)

- s = 307 meters = 1010 ft.



As a second issue, I'm wondering if anyone has measurements of
the typical strain on a winch or auto tow rope. I'm
guessing .5 to .9 times the glider weight (probably near the
highest altitude right before release, right?).

Strain during winch launch can easily be calculated by the weak link:
If a Ka-8 (weight 600 lbs) manages to break a weak link of 1.000 lbs,
maximum strain is 1.000 lbs. Maximum strain happens during the initial
acceleration of a heavy glider when still on the ground and in the
phase of maximum climb angle (usually between 300 and 900 ft).


Bye
Andreas

The stall 'horn' in the Katana DA20-C1 is nothing more
than a hole in the leading edge that at the right angle
'whistles'. Quite effective I might add too! Ready
to get the drill out for your leading edges;')


Or use the string AOA idea. I'd like to see this work.
I'm
not so keen on having something else the pilot has
to
LOOK at (vs. hearing). But who knows, and it's a fun
experiment...
--

------------+
Mark Boyd
Avenal, California, USA

Owain Walters wrote in message ...


Which brings us kind of full circle. The argument is
not against the World Class just against the requirements
and in turn against the PW5.

Or in other words, against the original concepts of the class. Even
though you have no interest in flying it, or letting those that do fly
it do so without a lot of unneeded derision.

As a former 1-26 owner, why am I not surprised?

Soaring is going to die a well deserved death, killed from within, not
from outside influence.